Ultrasonic atomiser



Nov. 15, 196 H. M. BUTTERWORTH ET AL 3,285,517

ULTRASONIC ATOMISER Filed March 12. 1965 FIG.2

INVENTORS HAROLD M. BUTTERWORTH ERNEST A NEPPIRAS BY j'bwa /z.

AGENT United States Patent 3,285,517 ULTRASONIC ATOMISER Harold Millman Butterworth, Crawley, and Ernest Arthur Neppiras, Reigate, England, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Mar. 12, 1965, Ser. No. 439,358 Claims priority, application Great Britain, Mar. 25, 1964, 12,611/64 2 Claims. (Cl. 239102) The invention relates to an ultrasonic atomiser, more particularly to a liquid fuel atomiser for boilers.

The greatest difficulties in designing ultrasonic atomisers resides in the production of sufficiently high vibration intensities and in ensuring that substantially the whole quantity of fuel supplied to the atomiser is really atomised. Additional problems are:

(a) The reduction of noise, which is particularly important in liquid-fuel driven domestic central heating systems,

(b) Obtaining a satisfactory operation in a reasonably wide range of fuel flow rates,

(c) Ensuring as far as possible a substantially uniform droplet size.

The ultrasonic fuel atomiser according to the invention comprises an electromechanical energy transducer, a velocity transformer for stepping up the velocity, having a larger limb 'being in acoustical and mechanical contact with the transducer and a sleeve surrounding a thinner limb of the transformer with a clearance space therebetween, and means for injecting the fuel to be atomised into the clearance space between the thinner limb and the sleeve in order to cause the liquid to flow along the thinner limb towards the free end face thereof.

The invention is characterized in that the sleeve consists of, or the inner wall of the sleeve is lined with, an acoustically absorbing material. The sleeve has preferably a smaller length than the transformer limb surrounded thereby and the absorbing material preferably consists of an expanded, synthetic material, for example foam rubber having a closed cell structure.

The invention will now be described more fully with reference to the accompanying drawing, in which FIG. 1 is a side elevation and partly a sectional view of an ultrasonic fuel atomiser and FIG. 2 is a front view of the device of FIG. 1.

As is shown in FIG. 1, the electromechanical transducer 1 is of the magnetostrictive type, which is in mechanical and acoustical contact with the thicker limb 2 of a cylindrical step-up velocity transformer, tuned to the vibrations and having a thinner limb 3, the free end of which has a substantially semi-hemispherical shape. The limb 3 is surrounded by a sleeve 4, which has, in the embodiment shown, a flange-shaped end 5 and is secured in a liquid-tight manner to the radial head face of the transformer limb 2 by means of screws 6. The front end of the sleeve 4 is provided with a mouth 7, the central opening of which has a given clearance X (FIG. 2) with respect to the limb 3.

Liquid, for example oil is supplied through a pipe 8 adjacent the rear side of the sleeve 4 near the thicker limb 2, so that the limb 3 is washed by liquid. The thick- "ice ness (Y) of the mouth 7 may be chosen so that at the non-supported end the sleeve 4 has sufiicient rigidity and the length of the sleeve together with the mouth 7 is preferably such that a distance Z between the mouth 7 and the centre of curvature of the hemispherical end of the limb 3 is obtained. It has been found that in this Way the mouth does not affect the atomized liquid at high flow rates.

It has been found, that the construction described above may be materially improved by making the sleeve 4 from acoustically, absorbing material or by providing a lining in the sleeve 4 of said material. Suitable materials are for example foam polystyrene, foam neoprene or natural or synthetic rubber of closed cell structure. From experiments it has been found that by using an absorbing lining the ultrasonic useful effect is improved by 30% and the noise is reduced. It has furthermore been found that a greater uniformity in droplet size is obtained.

Probably the lining reduces the formation of bubbles in the liquid within the space between the limb 3 and the sleeve 4, while noise absorption and scattering characteristics thereof suppress the effect of standing waves. In this way it can be ensured that the liquid flows in a more homogeneous stream to the vibrating hemispherical end face of the limb 3. Moreover, the spherical end of the limb 3 exhibits a greater movement of vibration excursion than the sleeve 4, since the latter is connected with a portion of the limb 2 of a larger diameter than the limb 3, so that it is subjected to a less great velocity transformation.

It will be obvious that the invention is not restricted to the device described above and that modifications for matching various practical circumstances are possible. The transducer may for example be a piezoelectric transducer and the velocity transformer may be constructed as a substantially exponential transformer instead of forming a step-up transformer. The vibrating end face need not be accurately hemispherical.

What is claimed is:

1. An ultrasonic liquid atomizer comprising an electromechanical energy transducer means, a velocity transformer having one end coupled with said transducer means, said transformer having an output limb defining a free end face, a sleeve member, means supporting said sleeve member for surrounding said output limb and defining a clearance space there between, means in said sleeve remote from the free end face of said output limb for admitting a liquid to be atomized into said clearance space, said sleeve member having an acoustical absorbing material defining said clearance space with said output limb, and said free end face of said output limb projecting beyond said sleeve member.

2. An ultrasonic atomizer according to claim 1 wherein said free end face is defined by a substantially semi-hemispherical surface having its center of curvature space axially beyond the adjacent end of said sleeve member.

References Cited by the Examiner UNITED STATES PATENTS 3,145,931 8/1964 Cleall 239-102 EVERETT W. KIRBY, Primary Examiner. 

1. AN ULTRASONIC LIQUID ATOMIZER COMPRISING AN ELECTROMECHANICAL ENERGY TRANSDUCER MEANS, A VELOCITY TRANSFORMER HAVING ONE END COUPLED WITH SAID TRANSDUCER MEANS, SAID TRANSFORMER HAVING AN OUTPUT LIMB DEFINING A FREE END FACE, A SLEEVE MEMBER, MEANS SUPPORTING SAID SLEEVE MEMBER FOR SURROUNDING SAID OUTPUT LIMB AND DEFINING A CLEARANCE SPACE THERE BETWEEN, MEANS IN SAID SLEEVE REMOTE FROM THE FREE AND FACE OF SAID OUTPUT LIMB FOR ADMITTING A LIQUID TO BE ATOMIZED INTO SAID CLEARANCE SPACE, SAID SLEEVE MEMBER HAVING AN ACOUSTICAL ABSORBING MATERIAL DEFINING FREE END FACE OF SAID OUTPUT LIMB PROJECTING BEYOND SAID SLEEVE MEMBER. 